Adjustable bracket structure



United States Patent Inventors Jacob A. Mehr Kirkwood, Mo.; Edna A. Mehr, Administratrix, Kirkwood, Mo. Appl. No. 740,420 'Filed May 31, 1968 Patented Dec. 15, 1970 Assignee Dazor Manufacturing Corp a corporation of Delaware ADJUSTABLE BRACKET STRUCTURE 12 Claims, 19 Drawing Figs.

US. Cl. 248/280, 248/123 Int. Cl A47f 5/00 Field of Search 248/280,

[56] References Cited UNITED STATES PATENTS 2,200,5 I 8 5/1940 Perbal 248/280 2,470,284 511949 Bergmans et al. 248/280 2,665,102 1/1954 Perbal 248/280 3,426,190 2/1969 Bobrick 240/73 Primary Examiner Roy D. Frazier Assistant Examiner-J. Franklin Foss Attorney-Cohn and Powell PATENTED DEC] 5 I970 SHEET 1 UF 4 v 7 JA 005 MfH/P, DECEASED,

BYfD/V/i A.MHl?, ADMIN/STRATRIX ATTORNEYS PATENTED um 5|97G 3547.390

SHEET u 0F 4 JACOB A. MEHR, DECEASED, BY EDA/4 A. MEHP,ADMINISTPATRIX ATTORNEYS ADJUSTABLE BRACKET STRUCTURE BACKGROUND OF THE INVENTION This invention relates generally to an adjustable bracket, and more particularly to a bracket adapted to carry a substantially constant load at variable distances from a support.

Adjustable brackets exist in the prior art which, in common with the present bracket, may carry a substantially constant load at a variable distance from a fixed support: adjustable lamp brackets are an example. However, the load carried at the end of the articulated arm of such brackets is of the order of 2 or 3 pounds. The load carried by such brackets in relation to the maximum extension of the arm is comparatively small. In one commonly used lamp, the extension is perhaps 25 inches and the load carried is only about 2 pounds.

Such lamp brackets work well within the .range of their intended use. However, the counterbalancing units of such arms are unsuitable for balancing the much greater moments which are resisted by the present device.

Although it is probably theoretically possible to increase the size of counterbalancing units on such existing brackets to cater for greater loads, practically speaking, very great problems are encountered when this is attempted. The combination of increased load-carrying capacity and increased extension would require a counterbalancing unit out of all proportion to the size of the bracket as a whole.

SUMMARY OF THE INVENTION By utilizing a modified linkage system for the arm, and connecting the arm to a compensating rocker assembly, the capability of the adjustable bracket is increased while retaining compactness. For example, the present device is admirably adapted to utilize the great load-carrying capacity of highstrength compression springs. This becomes possible because of the unique arrangement of parts.

One embodiment of the adjustable bracket has been adapted to carry the load of a television set and this particular bracket has a reach of about 50 inches. Thisrepresents a resistance moment capability of most times that of the lamp brackets discussed above.

Moreover, because of the parts employed and the arrangement of such parts, in particular the compensating rocker, the

increased reach and the improvement of the load-carrying capacity of the present adjustable bracket may be made even greater without substantial increase in the size of the counterbalancing unit. In addition, the proportions of the arm of the bracket are such as to enable nested channels to be used rather than circular rods. This feature facilitates the pivoting of the various parts and immeasureably enhances the appearance of the bracket.

The adjustable bracket includes an elongate adjustable arm having an inner end and an outer end, the arm being pivotally attached to a support between its ends. The other end of the arm is adapted to carry a load. A compensating rocker, including opposing arms, is pivotally connected to the support. The elongate arm is operatively interconnected at its inner end to one of the rocker arms, and resilient means operatively attached to the other rocker arm substantially counterbalance the load.

The elongate arm includes a pair of substantially parallel elongate links interconnected at associated ends by a pair of relatively short links, to form a parallel linkage system. The elongate links comprise opposed, nested channel-shaped members which form a substantially closed box section of variable width, the lower channel arm being pivotally connected to the support between its ends at a distance from the inner end substantially equal to the length of the short link at the inner end. An extension arm is attached to the short link at the outer end of the elongate arm to provide the load-carrying means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a general view of the adjustable bracket supporting a load;

FIG. 2 is a plan view of the adjustable bracket;

FIG. 3 is an enlarged cross-sectional view of the adjustable arm taken on line 3-3 of FIG. 1;

FIG. 4 is an enlarged cross-sectional view of the extension arm taken on line 4-4 of FIG. 1; I

FIG. 5 is a fragmentary cross-sectional view taken on line 5-5 of FIG. 2 illustrating the elbow joint between the adjustable arm and the extension arm;

FIG. 6 is an enlarged fragmentary cross-sectional view taken on line 6-6 of FIG. 1 illustrating the stabilizer;

FIG. 7 is a cross-sectional.viewtaken on line 7-7 of FIG. 5 further illustrating the stabilizer;

FIG. 8 is an enlarged fragmentary view of the end of the lower member of the adjustable arm at the elbow joint;

FIGS. 9, l0 and 11 are enlarged fragmentary, elevational views of the side, rear and front respectively of the support and counterbalance mechanism; 1

FIG. 12 is a cross-sectional view taken on line 12-12 of FIG. 9 illustrating the pivotal connection between the adjustable arm and the support; I

FIG. 13 is an enlarged fragmentary view of the pivotal slot of the support standard;

FIGS. 14 and 15 are enlarged, fragmentary plan views of the support from the upper side and the under side respectively;

FIG. 16 is a fragmentary cross-sectional view taken on line 16-16 of FIG. 11 illustrating the compensating rocker assembly;

FIG. 17 isa fragmentary view taken on line 17-17 of FIG. 9 further illustrating the pivotal connection between the adjustable arm and the support; 7

FIG. 18 is a cross-sectional view on line 18-18 of FIG. 10 illustrating the compensating rocker mechanism; and

a FIG. 19 is a diagrammatic illustration of the linkage and rocker mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now by characters of reference to the drawings,

and first to FIGS. 1 and 2, it will be understood that the ad-- elongate links, and a pair of short links 13 and 14 (FIGS. 5 and The compensating rocker arms are disposed in angular relation to each other, the included angle being between 90 and I80. An elongate pull link operatively interconnects the inner attachment means 16 16) interconnecting associated ends of the channel members 11 and 12. The channel members 11 and 12 are substantially parallel, and as shown in FIG. 3, the lower channel 12 is nested within the upper channel 11.

In the preferred embodiment, the elongate links 11 and 12 and the short links 13 and 14 cooperate to provide a substantially parallelogram linkage system. It will be understood, however, that the use of the phrase parallelogram-shaped is essentially a convenience and that departure from this shape is possible as long as two relatively long linksand two relatively short links are used.

The box-shaped extension arm 15, constituting a load-carrying means, is attached to the link 13 at the outer end of the elongate arm 10. The extension arm 15 is preferably, substantially the same length as the elongate arm 10, and includes an at its outer end supporting a frame 17,

which is adapted to carry a load 20 such as a television set or the like.

The elbow joint 21 between the elongate arm 10 and the extension arm 15 is shown in detail in FIG. 5. The upper channel 11 is pivotally connected to the link 13 by means of a pin 22 extending between the channel flanges 23 as shown in FIG. 6. The pin 22 is provided with retaining bosses 25 at each end.

The lower channel 12 is pivotally connected to link 13 by means of a pin 26 which extends between the channel flanges 27 nested within the channel flanges 23, sufficient clearance being provided between the ends of the pin 26 to allow movement of the lower channel 12 within the upper channel 11. It will be observed from FIG. 8 that the lower channel 12 is notched at its end 30 to provide clearance for the pin 22 as the extension arm 15 pivots about the pin 26 and induces movement into the upper arm 11.

A cover belt 30 (FIG. made of spring material is attached to the extension arm 15 and serves the purpose of providing a closure as the elbow joint 21 opens up. Such opening occurs when the angle between the elongate arm and the extension arm is more acute than illustrated in FIG. 5. This cover belt 30 is omitted for clarity in FIG. 6.

In order to control the relative looseness of movement between the upper and lower channels 11 and 12, a stabilizer 31 is provided to permit variation between the frictional engagement of the nesting channels 11 and 12. The stabilizer 31 is best shown by reference to FIGS. 5 and 7, and includes a V- shaped wedge member 32 which is threadedly connected to a screw 33. By turning the screw, the V-shaped member 32 may be moved inwardly or outwardly relative to the lower channel 12. A pair of opposing nylon plugs 34 are inset into the side flanges of the lower channel 12, each plug 34 having an inwardly facing wedge face. It will be understood that as the screw is turned to draw the wedge member 32 inwardly of the channel 12, the nylon plugs 34 are forced laterally against the flanges of the upper channel 11, thereby increasing the frictional engagement between the nested channels 11 and 12.

Referring now to the inner end of the elongate arm 10, it

will be understood that the arm 10 is pivotally connected to the support generally indicated by numeral 35 in FIGS. 1 and 2, and that the mechanism is covered by a housing 38. The inner end connection of the elongate arm 10 to the support is shown in detail in FIGS. 9 and 16. FIG. 16 clearly illustrates the pivotal relationship between the upper and lower channel members 11 and 12, which are interconnected by means of the short link 14. A pivot pin 36, extending between the flanges of the upper channel member 11, pivotally connects one end of the short link 14 to the upper channel 12, and a pivot pin 37, extending between the flanges of the lower channel 12, pivotally connects the other end of the link 14 to the lower channel 12. It will be observed that the lower channel 12 is notched at its end 40 to provide clearance for the pin 36 as the upper and lower channels 11 and 12 move relative to each other. It will be understood that the notched end 40 may be so shaped as to provide stop means limiting movement of the channel members 11 and 12 relative to each other and hence, limiting movement of the elongate arm 10 as a whole.

FIG. 19 illustrates diagrammatically the interrelationship between the elongate links 11 and 12 and short links 13 and 14 in the preferred embodiment.

As shown in FIGS. 9 and 12, the elongate arm 10 is pivotally supported by a standard 39 which includes a pair of opposing parallel side plates 41. The standard 39 forms part of the support 35. The pivotal support of the elongate arm 10 is accomplished by the provision of a relatively wide, substantially channel-shaped, auxiliary platform member 42, which is attached to the underside of the lower channel 12 as by set screws 47. The platform member 42 includes opposing parallel side flanges 43 which are disposed laterally outward of the side flanges 27 of the lower channel 12 to form lugs cooperating with parallel side plates 41. A trunnion-bushing 45 is attached, as by welding, to each of the side flanges 43, and a pair as a saddle journal bearingfor the pivot of slots 50, at the upper end of the side plates 41, provides a journal rotatively mounting each trunnion-bushing 45. The journal slots are clearly shown in FIG. 13.

A stop rod 51 extending between the inner faces of the side plates 41 provides a safety stop limiting movement of the arm 10 and also provides a connection between the two side plates 41 thereby strengthening the standard 39. The side plates 41 are also connected at their lower end by a cross plate 71 which will be referred to in greater detail later. This cross plate 71 forms the bight of the standard 39 which is substantially channel-shaped in overall configuration.

From FIG. 16 it can be seen that the adjustable elongate arm 10 is operatively attached to a pair of substantially similar compensating rocker arms 52 by means of a pair of elongate link bars 53 which are disposed outwardly of each of the compensating rocker arms 52 and on either side of the elongate arm 10. The pin 36, which connects the link 14 to the upper channel member 11, is extended outwardly beyond each of the side flanges of the channel member 11 to form a pivotal connection to the upper end of each elongate link 53. This arrangement is shown in FIG. 17.

The lower end of each link 53 is pivotally connected to one of the compensating rocker arms 52 by means of a pivot pin 54 which interconnects the link members 53, each compensating rocker arm 52 being provided with a slot 55 which-serves pin 54. A portion of each link 53 is notched at its upper end, as shown generally by numeral 55, to provide clearance for the pivot pin 37. Likewise, the bight portion of the channel-shaped platform member 42 is notched to clear each link 53. This notch is generally shown by numeral 56 in FIG. 14, which is a plan view of the support 35 from the upper side.

The U-shaped standard 39 is joggled at its midportion so that the side plates 41 are wider apart inthe upper section to provide adequate clearance for the pivotal movement of the elongate links 53. The relatively narrow space between the legs of the standard at its lower portion is occupied by the two compensating rocker arms 52. The pair of compensating rocker arms 52 are mounted to the standard by means of a rocker pin 57 which extends between the side plates 41. The rocker arms 52 are spaced apart by the base pivot 60. The base pivot 60 is attached to the standard 39 by means of a bolted connection 61 and in addition, the base pivot 60 is received at its upper end 62 in an aperture 63 provided in the rocker shaft 57. The standard 39, and therefore the adjustable arm as a whole, is firmly secured by couple connection to the base pivot 60.

A threaded rod provides an adjustable link 64, pivotal with respect to the compensating rocker arms 52, and operatively interconnecting the rocker arms 52 to a spring-balancing means. At its lower end, the adjustable link 64 is threadedly received by a short shaft 65. The shaft 65 is received in a slot 66 provided in each rocker arm 52. The slots 66 provide shaft 65 with a saddle journal bearing. The adjustable link 64, because of this arrangement, is free to rotate relative to the compensating rocker arm 52.

It will be understood that in FIG. 16, the compression springs which provide the resilient counterbalancing means are omitted for clarity. The counterbalancing system, will therefore be discussed with reference to FIG. 10, in conjunction with FIGS. 9 and 16. With regard to the counterbalancing.

system, it will be understood from FIG. 10 that the cross plate 71 which forms the bight of the standard 39 is extended outwardly beyond the outer faces of the side plates 41 to provide a pair of spring-holding extension portions 72 supporting the base of each spring 70.

Each spring holder 72 is provided with an aperture 73 threadedly receiving a spring guide rod 74. The spring guide rods 74 are fixed in position relative to the spring holders 72 and, therefore, each compression spring which is mounted, on one of the guide rods 74 must move substantially of that guide rod 74 when compressed.

Precompression can be applied to the. springs 70 through the medium of a pressure plate 75 which is susceptible of movement axially of the guide rods 74 by means of a swivel nut 67, the nut 67 being threadedly adjustable relative to the adjustable link 64.

Precompression of the springs 70 results in an upward pull on the adjustable link 64, the springs 70 thereby counterbalancing the load applied to the end of the load-carrying extension arm as will later appear.

Referring again to FIG. 16, it will be understood that the swivel nut 67 allows the adjustable link 64 to be moved out of parallel alignment with the spring guides 74. This movement occurs as the rocker arms 52 rotate, thereby causing the lower end of the adjustable link 64 to follow the orbital rotation of the shaft 65 relative to the rocker arm shaft 57. In this regard, it is convenient to consider each of the compensating rocker arms 52 as having an effective length equal to thedistance between the center of the rocker arm shaft 57 and the centers of rotation of the shaft 65 and the pivot pin 54 respectively. These hypothetical arms are represented'by the broken lines 76 and 77 for convenience.

The pressure plate 75 is provided with an aperture 78 having a compatible surface with the curved surface of the swivel nut 67, whereby to effectuate the swiveling action of the swivel nut 67.

The housing 38 (FIG. 9) is attached to the support 35 by means of set screws 40 threadedly connected to the upper and lower ends of each of the spring guide rods 74. It will be understood that the housing 38 conceals the working parts of the support 35 to present a pleasing and compact appearance.

It is believed that the functional interrelationship of the various parts of this adjustable bracket have become apparent from the foregoing description of parts. For completeness of disclosure, however, the operation of the bracket as a whole, will be briefly described with particular reference to the diagrammatic representation of the linkage as shown in FIG. 19. It is to be understood that FIG. 19 illustrates two positions of the adjustable elongate arm 10. The full lines are representative of the arm 10 in a median elevation, and a somewhat extended position. The broken lines are representative of the arm 10 in a raised position which, for the sake of facilitating the discussion, will be assumed to result in the pivot pin 54 being at its lowest position (54). Further, when the compensating rocker arms 52 are in the position indicated by the broken lines, coincident with the low point 54 of the pivot pin 54, the swivel nut 67, at the upper end of the adjustable link 64, is at its high point as indicated by 67'. For'convenience in the following discussion it will be assumed that the system is one-dimensional. The various components will be referred to in the singular, although for practical reasons some components are paired.

When a load is applied to the end of thel'oad-carrying extension am 15, the swivel nut 67, will tend to move downward because of the interconnecting linkage. In order to prevent this downward movement, an upward balancing force P, the amount of which depends upon the leverage of the system, must be applied. This upward force P is provided by the spring 70.

The spring 70 has an unstressed length equal to L. By compressing the spring 70 a distance I and attaching it to the swivel nut 67 at location 67'the spring 70 will be precompressed to the value of P. P is equal to the spring rating r multiplied by distance I .The upward force P resulting from precompression of the spring 70 balances the downward force W caused by the load 20. With the adjustable arm 10 disposed as respresented by the broken line, therefore, the system is balanced.

If the adjustable arm 10 is now moved to a different position, such as that shown by the full lines, the vertical component of the force in the pull rod 53 will be substantially unchanged under certain conditions. These conditions exist when the proportions of the parallelogram linkage of the extension arm 10 are properly chosen so that movement of attachment means 16 toward pivot trunnion 45 is proportional to movement of pivot pin 36 toward pivot trunnion 45.

When the length of the link 53 is relatively long, the balancing of moments about the rocker arm 52 becomes largely a matter of balancing vertical forces. That is, balancing of moments about the center of the rocker arm 52 is primarily dependent upon the balancing of the vertical forces in the pull rod 53 and the spring 70, taking their respective moment arms into consideration.

As the rocker arm 52 is rotated from one position to the other, spring 70 is compressed further distance e. However, because the angular relationship between the rocker arms 76 and 77 is substantially less than l80the moment arm of the vertical component of the increased spring load decreases substantially. The result of this is that the system remains substantially in balance.

On the pull rod side of the rocker arm 52, the variations in load and moment arm of the pull rod 53 are slight, resulting in small change of moment. On the spring side of the rocker arm 52, the variations in load and moment arm are considerable but, because of the rocker arm configuration, are compensatory.

In the preferred embodiment, the elongate links 11 and l2 are substantially parallel and the same length, and the short lengths l3 and 14 are likewise substantially parallel and the same length, resulting in a parallelogram linkage system. The length of the arm 15 between pivot pin 26 and pivoted attachment means 16 is preferably the same as the length of the arm 12 between pivot trunnion 45 and pivot pin 26. Likewise the length of arm 12 between pivot trunnion 45 and pivot pin 37 is substantially the same as the length of the links 13 and 14 between pivot pins. These relationships, though not essential, result in a substantially balanced elongate arm 10 and loadcarrying arm 15.

The principles as described have been somewhat simplified. Obviously, secondary moment forces and forces due to the weight of the various parts of the structure itself have an effect on the balancing. However, these second effects are provided for by the friction which is encountered between the various joints. Moreover, the provision of the stabilizer 31 between the arms 11 and 12 creates a built-in frictional control which may be varied as desired.

It is claimed:

1. An adjustable bracket comprising:

a. a support;

b. an elongate adjustable arm including an inner end and an outer end;

c. means pivotally connecting the inner end of the arm to the support;

(1. load-carrying means at the outer end of the support adapted to carry a load;

e. a compensating rocker including a pair of arms pivotally connected to the support at a pivot axis;

f. means operatively interconnecting the inner end of the elongate arm to one rocker arm in spaced relation to the pivot axis; and

. resilient means operatively attached-to the other rocker arm in spaced relation to the pivot axis and in spaced relation to the connection of the inner end to' the rocker, whereby to substantially counterbalance the load;

h. the compensating rocker including a pair of arms disposed in angular relation to each other, the pivot axis being located substantially between the arms;

i. the elongate arm including a pair of elongate links and a pair of relatively short links, one of said short links pivotally connecting associated ends of the elongate links at the inner end of the elongate arm, and the other of said short links pivotally connecting associated ends of the elongate links at the outer end of the elongate arm.

2. An adjustable bracket as defined in claim 1, in which;

j. the compensating rocker arms disposed in angular relation to each other have an included angle between the arms of between and 1 3. An adjustable bracket as defined in claim 1, in which: the

means operatively interconnecting the inner end of the elongate arm to said one rocker arm include an elongate link.

4. An adjustable bracket as defined in claim 1, in which:

j. the means operatively interconnecting the inner end of the elongate arm to said one rocker arm include an elongate pull link; and

k. another elongate link operatively connects the resilient means to said other rocker arm.

5. An adjustable bracket as defined in claim 1, in which:

j. the resilient means includes an elongate helical spring supported at one end by the support; and

k. an elongate link operatively connects the other end of the spring to said other rocker arm.

6. An adjustable bracket as defined in claim 1, in which:

j. the compensating rocker arms are disposed in angular relation to each other and the included angle between the arms is between 90 and 180;

k. the means operatively interconnecting the inner end of the elongate arm to said one rocker arm'include an elongate link;

l. the resilient means includes an elongate helical spring supported at one end by the support;

m. an elongate link operatively connects the other end of the spring to said other rocker arm; and

n. guide means attached to the support predispose the spring to move in a predetermined direction 7. An adjustable bracket as defined in claim 1, in which:

j. the elongate links of the elongate arm are substantially parallel and include an upper link and a lower link;

k. the means pivotally connecting the inner end of the arm to the support include pivotal connection of the lower elongate link to the support at a point disposed between the interconnection points of said short links to said lower link;

. the intersection of the upper elongate link and shortlink at the inner end of the elongate arm form a pivot point disposed in variable spaced relation from the pivotal connection between the arm and the support; and

m. the means operatively interconnectingthe inner end of the elongate arm to said one rocker arm include an elongate pull link operatively interconnected to one of said intersecting links.

8. An adjustable bracket as defined in claim 7, in which: the pull link is pivotally interconnected to said intersecting links at their intersection point.

9. An adjustable bracket as defined in claim 1, in which:

j. the elongate links are formed from opposing nested channel members to form a substantially closed box section of variable width; and

k. the short link at the inner end of the elongate arm is independently movable relative to the support.

10. An adjustable bracket comprising:

a. a support;

an elongate adjustable arm including an inner end and an outer end;

c. means pivotally connecting the inner end of the arm to the support;

d. load-carrying means at the outer end of the support adapted to carry a load;

e. a compensating rocker pivotally connected to the support at a pivot axis;

f. means operatively interconnecting the inner end of the elongate arm to the rocker at a distance from the pivot axis;

g. resilient means operatively attached to the rocker in spaced relation to the pivot axis and the connection of the inner end to the rocker, whereby to substantially counterbalance the load;

h. the compensating rocker including opposing arms disposed in angular relation to each other, the pivot axis being located substantially between the arm;

i. the elongate arm includes a pair of elongate links and a pair of relatively short links, one of said short links pivotally connecting associated ends of the elongate links at the inner end of the elongate arm, and the other of said short links pivotally connecting associated ends of the elongate links at the outer end of the elongate arm;

b. an elongate adjustable arm including an inner end and an outer end;

c. means pivotally connecting the inner end of the arm to the support;

d. load-carrying means at the outer end of the support adapted to carry a load;

e. a compensating rocker pivotally connected to the support at a pivot axis;

f. means operatively interconnecting the inner end of the elongate arm to the rocker at a distance from the pivot axis;

g. resilient means operatively attached to the rocker in spaced relation to the pivot axis and the connection of the inner end to the rocker, whereby to substantially counterbalance the load;

h. the compensating rocker including opposing arms disposed in angular relation to each'other, the pivot axis being located substantially between the arms;

i, the elongate arm includes a pair of elongate links and a pair of relatively short links, one of said short links, pivotally connecting associated ends of the elongate links at the inner end of the elongate arm, and the other of said short links pivotally connectingassociated ends of the elongate links at the outer end of the elongate arm;

j. the elongate links of the elongate arm being substantially parallel and the short links being substantially equal in length; and

k. the means pivotally connecting the inner end of the arm to the support including pivotal connection of one of said elongate links to the support, at a point disposed from the inner end pivotal connection of that link to the short link, a distance substantially equal to the length of a short link.

12. An adjustable bracket comprising:

a. a support;

b. an elongate adjustable arm including an inner end and an outer end;

c. means pivotally connecting the inner end of the arm to the support;

d. load-carrying means at the outer end of the support adapted to carry a load;

e. a compensating rocker pivotally connected to the support at a pivot axis;

means operatively interconnecting the inner end of the elongate arm to the rocker at a distance from the pivot axis;

g. resilient means operatively attached to the rocker in spaced relation to the pivot axis and the connection of the inner end to the rocker, whereby to substantially counterbalance the load;

h. the elongate arm including:

l. upper and lower substantially channel shaped members, one nested within the other to form a substantially closed box section of variable width; and

2. a pair of relatively short links, one of said short links pivotally connecting associated ends of the upper and lower channel members at the inner end of the elongate arm, and the other of said short links pivotally connecting associated ends of the upper and lower channel members at the other end of the elongate arm;

. the load-carrying means including an extension arm attached to the short link at the outer end of the elongate arm;

j. the means pivotally connecting the inner end of the arm to the support including pivotal connection of the lower channel to the support at a point disposed between the connection point of said lower channel to said links;

k. the means operatively connecting the inner end of.:the elongate arm to the rocker including an elongate-pull link;

the other end of the spring to the rocker arm; and n. guide means attached to the support and predetermining the direction of movement of the helical spring. 

